Halogen-free ionic liquids in naphtha desulfurization and their recovery

ABSTRACT

Ionic liquids of the general formula C + A −  where C +  represents an organic cation, specifically, but not limited to the imidazolium, pyridinium, isoquinolinium, ammonium types, which have aliphatic and aromatic substituents, while A −  represents a carboxylate, aromatic and aliphatic anion. The ionic liquids are synthesized under conventional heating or microwave irradiation This invention is also related to the application of ionic liquids to remove sulfur compounds of naphthas through a liquid-liquid extraction and the recovery and reuse of ionic liquids by the application of heat, reduced pressure and washing with solvents.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the priority to Mexican Patent Application No.MX/a/2008/011121, filed on Aug. 29, 2008, in the Mexican Patent Office,the disclosure of which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is related to the synthesis of new halogen-freeionic liquids which are insoluble in hydrocarbon mixtures and with theproperty of dissolving aliphatic and aromatic sulfur-containingcompounds that contaminate the naphtha. In accordance with the presentinvention a desulfurization process is carried out by a liquid-liquidextraction process at room temperature and pressure.

Specifically, the invention is related to the synthesis of halogen-freeionic liquids and their application to remove sulfur-containingcompounds, in which ionic liquids are provided which have the generalformula C⁺ A⁻, where C⁺ represents an organic cation, especially but notexclusively of: alkylpyridinium, dialkylimidazolium,trialkylimidazolium, tetraalkylammonium and alkylquinolinium types,while the anion A⁻ represents carboxylate organic derivatives ofaliphatic and aromatic carboxylic acids, such as acetate, butanoate,stearate and benzoate, among others. Additionally, the invention coversthe regeneration and reuse of these ionic liquids by means of heating,reduced pressure and washing with solvents.

BACKGROUND OF THE INVENTION

The gases emitted by internal combustion engines represent the mainsource of atmospheric pollution and depend directly on the quality ofthe combustible used. Different actions have been carried out worldwidefor the production and refining of higher quality gasoline and diesel.For example, since 2005 the European Union set the upper limit of 50 ppmof sulfur in diesel and gasoline; however Germany has gone further andreduced to 10 ppm. For the United States of America the standard for themaximum content of sulfur in gasoline will be 80 ppm and 30 ppm asaverage. In Mexico, PEMEX (Pemex Refining), based on their commitment toproducing and distributing gasoline to comply with environmental lawsand international standards of quality, is adjusting its parameters toproduce gasoline, as a rule establishing maximum sulfur content between15 and 30 ppm from 2008 until 2010.

The most used treatment for desulfurization of gasolines in refiningprocesses is catalytic hydrodesulfurization at high temperature andpressure (HDS process) (I. Pachano, J. Guitian, O. Rodríguez, J. H.Krasuk (Intevep. S.A.) U.S. Pat. No. 4,752,376 (1988), Jr. Hensley, L.Albert, L. M. Quick, (Standard Oil Company) U.S. Pat. No. 4,212,729);however this process is very expensive and drastic conditions ofoperation are required, employing transition metal-containing catalyst,which lose their activity quickly, especially for heavy Mexican oilswith higher content of sulfur, which are very difficult for processingand for sulfur removal.

In some countries new Technologies have been developed for resolvingthis problem (Zaczepinski, S. Exxon Diesel Oil Deep Desulfurization(DODD) in Handbook of Petroleum Refining Processes, ed. R. A. Meyer,McGraw-Hill, NY, 1996, Cap. 8.7; Ito, E.; Rob, J. A.; Veen, R. V. Catal.Today 2006, 116, 446-460; Brunet, S.; Mey, D.; Pérot, G.; Bouchy, C.;Diehl, F. Appl. Catal. A 2005, 278, 143-172) for example the adsorptionof sulfur compounds under solid absorbent, this process is known asIRVAD® (U.S. Pat. No. 5,730,860, dated Mar. 24, 1998) from Black &Veatch Pritchard Inc., the process S Zorb® from Phillips Petroleum(http://www.eia.doe.gov/oiaf/servicerpt/ulsd/uls.html) and the processfrom Haldor Topsoe (EP 1057879, published date: Dec. 6, 2000); theliquid-liquid extractions with common organic solvents (PetrostarRefining, 217 National Meeting, American Chemical Society, Anaheim,Calif., March 1999) oxidative desulfurization with different oxidantagents (Unipure Corp., NPRA Meeting No AM-01-10, March 2001; SulphcoCorp, NPRA Meeting No AM-01-55, March 2001; BP Chemicals UK, Journal ofMolecular Catalysis A: Chemical (1997) 397-403; UOP LLC, U.S. Pat. No.6,171,478 dated Jan. 9, 2001; EXXON Research and Engineering Co., U.S.Pat. No. 5,910,440 dated Jun. 8, 1999, U.S. Patent Publication No.2002/35306A1 dated Mar. 21, 2002; Fuel 2003, 82, 4015; Green Chem. 2003,5, 639).

Ionic liquids have attracted the attention of research due to theirphysicochemical properties, such as: very low vapor pressure,non-flammability, non-corrosives, low toxicity and by these reason theyare excellent substitutes of common volatile organic solvents(Wasserscheid, P.; Keim, W. (Eds.) Ionic Liquids in Synthesis,Wiley-VCH, Wenheim, 2004; Welton, T. Chem. Rev. 1999, 99, 2071-2084;Zhao, H.; Malhotra, S. V. Aldrichimica Acta 2002, 35, 75-83) and promotetheir application in different oil refining processes and for chemicalindustry (Rogers, R. D.; Seddon, K. R (Eds.) Ionic Liquids: IndustrialApplications of Green Chemistry. ACS, Boston, 2002; Rogers, R. D.;Seddon, K. R (Eds.) Ionic Liquids as Green Solvent: Progress andProspects. (ACS Symposium Series), Boston, 2003; Rogers, R. D.; Seddon,K. R (Eds.) Ionic Liquids IIIB: Fundamentals, Progress, Challenges, andOpportunities: Transformations and Processes (ACS Symposium Series),Boston, 2005; Roger, R. D.; Seddon, K. R.; Volkov, S (Eds.). GreenIndustrial Applications of Ionic Liquids. (NATO Science Series), KluwerAcademic Publishers, Dordrecht, Netherlands, 2002).

One of the first publications that mention the use of ionic liquid forremoving mercaptans from hydrocarbon fluid is WO Publication No. 0234863with publication date May 2, 2002. The methods described are based onthe use of sodium hydroxide in combination of ionic liquids to favor theconversion of mercaptans in mercaptides, which are removed with ionicliquids. During the 2005-2009 years, Peter Wassercheid and coworkershave published several patents and papers about the ionic liquids forthe process of the deep desulfurization of hydrocarbons (Chem. Corn.(2001) 2494; WO 03037835 published May 8, 2003, U.S. Patent PublicationNo. 2005/0010076A1, published Jan. 13, 2005). In these works the authoremployed ionic liquids with general formula C⁺A⁻ where C⁺ is1,3-dialkyllimidazolium or tetraalkylamonium and A⁻ aretetrachloroaluminates or methanesulfonates. By means of a process withseveral and successive extractions (up to 8 extractions), high sulfurextraction efficiencies were achieved using model gasolines. However,the use of ionic liquids containing aluminum salts have the problem ofthe high acidity of chloroaluminates which leads to secondary reactionssuch as olefins polymerization, in addition ionic liquids containingthis anion type are highly hygroscopic and non-stables to atmospherichumidity.

U.S. Patent Publication No. 2003/0085156A1, published May 8, 2003, alsomakes mention of the use of ionic liquids where the quaternary ammoniumor alkylphosphonium are the cations and tetrachloroaluminate as anion.For the extraction of sulfur compounds in synthetic fuels, it ismentioned that these compounds can be oxidized to sulfoxides or sulfonesbefore or during the extraction process.

It was published in Energy & Fuels 18 (2004) 1862, that CuCl-based ionicliquids exhibited desulfurization ability of gasoline when used in anextraction process; as well as a published paper (Zhang, S.; Zhang, Q.;Conrad Zhang, Z. Ind. Eng. Chem. Res. 43 (2004) 614) some ionic liquidsproperties and sulfur and nitrogen compounds removal from transportationfuels were studied.

In U.S. Patent Publication No. 2004/0045874A1, published Mar. 11, 2004,a process for desulfurization and denitrogenation of hydrocarbonfractions using a wide family of ionic liquids was explored withalkylating agents of high efficiencies.

SUMMARY OF THE INVENTION

All above mentioned references are overcome by the present invention,because none of them claimed the use of ionic liquids containingaliphatic or aromatic carboxylate anions, which has the advantage thatit does not decompose during the desulfurization process and can beregenerated and reutilized in several consecutive extraction processes.Another object of the present invention is the utilization of theseionic liquids in the deep desulfurization of organic liquids and naphthaby a selective extraction of organosulfur compounds. It is important tomention that the term naphtha refers to a petroleum fraction constitutedby organosulfur compounds from C₄-C₉, with a concentration of 85-90% inweight, density of 0.64-0.85 g/cm³, preferably of 0.64-0.70 g/cm³,30-220° C., preferably of 30-140° C., and a content of total sulfur of100-500 ppm, preferably of 100-250 ppm.

Syntheses of ionic liquids of the present invention were carried out intwo steps, in the first step, an alkyl, alkenyl, benzyl oralkyl-functionalized halides (both chlorides and bromides) were placedto react with alkenyl, benzyl, or alkyl functionalized imidazoles,pyridines, isoquinoline or tertiary amines, while in the second step,anion interchange reaction happened between the ionic liquid with asilver carboxylate.

On the other hand, for the removal of sulfur compounds, a liquid-liquidextraction is made, which the ionic liquid naphtha is mixed with naphthaand is subjected to agitation, and then separates the two phases:desulfurized naphtha and the sulfured ionic liquid.

The present invention also encompasses a procedure for recovering theionic liquids in order that they can be used again to remove sulfurcompounds, this procedure involves three stages: the first providesheating at reduced pressure, in the second, they are performed washingswith organic solvents, and in the third, such solvents are removed undervacuum conditions.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to the synthesis and application ofionic liquids that have kind of carboxylate anions and are halogen-freeand remove efficiently sulfur compounds contaminants from naphtha.

The process of extraction and removal of sulfur compounds from a sulfurcontaining liquid is composed of the strong agitation of the two phases(ionic liquids and naphtha) followed by a process of separation ofphases, where the sulfur compounds pass to phase comprising the ionicliquid and as a result total sulfur content is considerably reduced inthe naphtha, this occurs due to the higher affinity of sulfur compoundsinto the ionic liquid compared with naphtha.

Ionic liquids used in the present invention have general formula C⁺ A⁻where C⁺ is an organic cation such as imidazolium, pyridinium,isoquinolinium and ammonium, and A⁻ is an anion-type organiccarboxylate, including aromatic and aliphatic substituents as shown inTable 1.

TABLE 1 Overall structure of cations and anions constituting the ionicliquids of this invention C⁺ (Cations)

Imidazolium

Pyridinium

Isoquinolinium

Quaternary ammonium A⁻ (Anions)

Carboxylate where: R, R₁, R₂ y R₃ are independently radicals representedby alkyl group, cycloalkyl group, alkenyl group, benzylic group andalkyl functionalized group, preferably these groups have from 1 to 10carbon atoms; R₄ comprises alkyl group, cycloalkyl group, alkenyl group,benzylic group and alkyl functionalized group, preferably these groupshave from 1 to 18 carbon atoms.

In one aspect of the invention, a process for the desulfurization of anorganic liquid includes the steps of contacting the organic liquid withthe ionic liquid having the formula C⁺ A⁻, where C⁺ and A⁻ are asdefined above. The desulfurization is carried out by a liquid-liquidextraction where the sulfur compounds are recovered in the ionic liquid.The ionic liquid is immiscible with the organic liquid which results ina phase separation. The organic liquid can be, for example, naphtha, asdefined above, gasoline, diesel fuel, kerosene, heating oil and otherpetroleum based liquids.

EXAMPLES Synthesis of Ionic Liquids of this Invention

Synthesis of halogen-free ionic liquids of this invention was conductedin the following two stages using the methods described in theliterature (Saravanabubu M, Wiencek J M, Ren R X, Linhardt R J.Carbohydr. Polymer 63 268-271 (2006); Brindaban C R and Subas B. Org.Lett. 7 3049-3052 (2005).

First Step.

Ionic liquid was synthesized by reaction of alkyl, alkenyl, benzyl oralkyl-functionalized chlorides and bromides, with organic nitrogencompounds such as imidazole, pyridine, isoquinoline and tertiary amines.

Second Step.

An anion exchange performed by the reaction of the respective ionicliquid with a silver carboxylate, resulting in a silver halide whichprecipitates and is separated from the reaction by filtration

Both steps were prepared using both conventional heating and microwaveoven; the last heating method produces ionic liquids with higher yields(5 to 9%) and in shorter times (95 to 99%) than the first one.

The syntheses of the present invention are illustrated by thepreparation of eight ionic liquids named LI 1, LI 2, LI 3, LI 4, LI 5,LI 6, LI 7 y LI 8 respectively, but it does not mean some restriction.The preparation procedure is exemplified by the synthesis of1-hexyl-3-methyl-imidazolium acetate (LI-1), using two differentmethods, conventional and microwave heating.

Example 1 Synthesis of 1-hexyl-3-methyl-imidazolium acetate (LI-1)Method 1 Conventional Heating

First step: An oven-dried, 100-mL, three-necked, round bottomed flaskequipped with a magnetic stirring bar, thermometer and a refluxcondenser is charged with 20 mmol 1-methyl-imidazole and 60 mmol of1-bromohexane, the resulting solution was heated at 80° C. for 24 hr. Atthe end of this time, two phases were produced, the upper phase wasdecanted and the lower phase, which contained the ionic liquid, waswashed with ethyl acetate (3×20-mL). The solvent was eliminated atreduced pressure.

Second step (Anion interchange): An oven-dried, 100-mL, three-necked,round bottomed flask equipped with a magnetic stirring bar, thermometerand a reflux condenser, were dissolved 10 mmol of1-hexyl-3-methyl-imidazolium bromide obtained in first step, in 50-mL ofacetonitrile. Silver acetate (10 mmol) was slowly added to the solution.The mixture was refluxed for 10 hr, and then the precipitated wasfiltered off, the ionic liquid was dried under vacuum conditions and itwas obtained a yellow liquid.

Synthesis of 1-hexyl-3-methyl-imidazolium acetate (LI-1) Method 2Microwave Heating

First step: An oven-dried, 100-mL, one-necked, round bottomed flaskequipped with a magnetic stirring bar, and a reflux condenser is chargedwith 20 mmol of 1-methyl-imidazole and 60 mmol of 1-bromohexane, theresulting solution was exposed to microwave irradiation in a CEMDiscover Labmate microwave oven (100 watts power) and heated at 80° C.for 10 min. At the end of this time, two phases were produced, the upperphase was decanted and the lower phase, which contained the IL, waswashed with ethyl acetate (3×20-mL). The solvent was eliminated atreduced pressure.

Second step (Anion interchange): An oven-dried, 100-mL, one-necked,round bottomed flask equipped with a magnetic stirring bar, and a refluxcondenser, were dissolved 10 mmol of 1-hexyl-3-methyl-imidazoliumbromide obtained in first step, in 50-mL of acetonitrile. Silver acetate(10 mmol) was slowly added to the solution. The mixture was heated in aCEM Discover Labmate microwave oven (75 watts power) for 12 min; silverbromide was filtered off, the ionic liquid was dried under vacuumconditions and it was obtained a yellow liquid.

Examples 2 to 8

The ionic liquids of this invention were synthesized using two differentheating methods, the first one (conventional heating) and the second one(microwave heating). The interchange anion step was done using silvercarboxylate (acetate, benzoate, butanoate and stearate). The ionicliquids of this invention were characterized by spectroscopic ¹H and ¹³CNuclear Magnetic Resonance data, the chemical shifts are reported in ppmin d₆-DMSO and CDCl₃ with tetramethylsilane as an internal Standard.

The spectroscopic data and yields of the ionic liquids synthesized inthis invention are summarized as follows:

Yields and spectroscopic data of ionic liquids (1 to 8) Ionic Liquid 1(LI-1)

Example 1 Method 1 Yield 82% Method 2 Yield 90%1-hexyl-3-methyl-imidazolium acetate ¹H NMR (DMSO-d₆) δ 0.82 (t, J = 6.9Hz, 3H), 1.22 (m, 6H), 1.75 (sx, J = 5.6 Hz, 2H), 1.80 (s, 3H), 3.87 (s,3H), 4.18 (t, J = 7.1 Hz, 2H), 7.78 (dd, J₁ = 1.6 Hz, J₂ = 1.9 Hz, 1H),7.87 (dd, J₁ = 1.6 Hz, J₂ = 1.9 Hz, 1H), 9.39 (s, 1H) ppm. ¹³C NMR(DMSO-d₆) δ 14.3, 22.4, 22.9, 25.7, 29.9, 31.1, 36.3, 49.3 122.8, 124.1,137.2, 173.5 ppm. Ionic Liquid 2 (LI-2)

Example 2 Method 1 Yield 85% Method 2 Yield 91%1-octyl-3-methyl-imidazolium acetate ¹H NMR DMSO-d₆) δ 0.82 (t, J = 6.9Hz, 3H), 1.24 (m, 10H), 1.82 (sx, J = 6.8 Hz, 2H), 2.04 (s, 3H), 3.85(s, 3H), 4.15 (t, J = 7.0 Hz, 2H), 7.42 (dd, J₁ = 5.5, 1.1 Hz, 2H), 8.69(s, 1H) ppm. RMN ¹³C (75.4 MHz, DMSO-d₆) δ 13.6, 22.2, 22.7, 25.5, 28.3,28.4, 29.4, 31.2, 35.9, 49.8, 122.4, 122.7, 137.0, 175.0 ppm. IonicLiquid 3 (LI-3)

Example 3 Method 1 Yield 85% Method 2 Yield 90%1,2-dimethyl-3-octyl-imidazolium acetate ¹H NMR(CDCl₃) δ 0.87 (t, J =6.6 Hz, 3H), 1.26 (m, 10H), 1.81 (sx, J = 7.0 Hz, 2H), 2.04 (s, 3H),2.78 (s, 3H), 3.99 (s, 3H), 4.18 (t, J = 7.4 Hz, 2H), 7.45 (d, J = 2.0Hz, 1H), 7.67 (d, J = 2.0 Hz, 1H) ppm. RMN ¹³C (75.4 MHz, CDCl₃) δ10.3,13.6, 21.4, 22.2, 25.9, 28.6 (2C), 29.5, 31.3, 35.6, 48.6, 120.9, 122.7,143.4, 175.2 ppm. Ionic Liquid 4 (LI-4)

Example 4 Method 1 Yield 89% Method 2 Yield 95%1-benzyl-3-methyl-imidazolium acetate ¹H RMN (CDCl₃) δ 1.98 (s, 3H),4.02 (s, 3H), 5.52 (s, 2H), 7.33-7.51 (m, 7H), 10.43 (s, 1H) ppm. RMN¹³C (75.4 MHz, CDCl₃) δ 22.6, 36.5, 53.2, 121.8, 123.7, 128.8 (2C),129.4 (3C), 133.4, 138.2, 175.6 ppm. Ionic Liquid 5 (LI-5)

Example 5 Method 1 Yield 89% Method 2 Yield 95%1,2-dimethyl-3-butyl-imidazolium benzoate ¹H RMN (CDCl₃) δ 0.82 (t, J =7.2 Hz, 3H), 1.20 (sx, J = 7.6 Hz, 2H), 1.55 (qi, J = 7.4 Hz, 2H), 2.47(s, 3H), 3.71 (s, 3H), 3.87 (t, J = 7.4 Hz, 2H), 7.22-7.32 (m, 5H), 7.97(dd, J₁ = 8.2, 1.6 Hz, 2H) ppm. RMN ¹³C (75.4 MHz, CDCl₃) δ 9.6, 13.4,19.5, 31.6, 35.3, 48.3, 121.0, 123.1, 127.6, 129.5, 130.1, 137.3, 143.3,171.1 ppm. Ionic Liquid 6 (LI-6)

Example 6 Method 1 Yield 83% Method 2 Yield 91% Butyl-isoquinoliniumbutanoate ¹H RMN (CDCl₃) δ 0.82 (t, J = 7.5 Hz, 3H), 0.95 (t, J = 7.2Hz, 3H), 1.30 (m, J = 7.6 Hz, 6H), 1.7 (m, J = 7.2 Hz, 2H), 2.1 (t J =6.0 Hz, 2H), 2.3 (t, J = 7.2 Hz, 2H), 5.0 (t, J = 6.0 Hz, 2H), 7.5-7.86(m, 5H), 8.5 (s, 1H), 9.15 (s, 1H) ppm. RMN ¹³C (75.4 MHz, CDCl₃) δ13.8, 14.1, 18.6, 22.3, 25.9, 28.8, 31.1, 36.1, 61.9, 120.4, 126.4,127.15, 128.63, 130.2, 135.7, 142.9, 152.4, 173.8 ppm Ionic Liquid 7(LI-7)

Example 7 Method 1 Yield 78% Method 2 Yield 89%Dimethyl-diethyl-ammonium stearate ¹H RMN (CDCl₃) δ 0.9 (s, 3H), 1.39(t, J = 7.26 Hz, 6H), 1.5 (m, 28H), 1.6 (m, 2H), 2.28 (m, 2H), 2.92 (s,6H), 3.34 (c, J = 7.14 Hz, 4H), ppm. RMN ¹³C (75.4 MHz, CDCl₃) δ 7.8,14.1, 22.7, 25.0, 29.3, 29.7, 32.0, 34.1, 49.16, 60.1, 174.8 ppm IonicLiquid 8 (LI-8)

Example 8 Method 1 Yield 83% Method 2 Yield 91% Butyl-pyridiniumbutanoate ¹H RMN (CDCl₃) δ 0.86 (t, J = 7.5 Hz, 3H), 0.95 (t, J = 7.2Hz, 3H), 1.24 (m, J = 7.6 Hz, 6H), 1.7 m, J = 7.2 Hz, 2H), 2.15 (t J =6.0 Hz, 2H), 2.4 (t, J = 7.2 Hz, 2H), 5.2 (t, J = 6.0 Hz, 2H), 8.23 (t,J = 6.0 Hz, 2H), 8.61 (t, J = 6.0 Hz, 1H), 9.62 (d, J = 6.0 Hz, 2H) ppm.RMN ¹³C (75.4 MHz, CDCl₃) δ 13.5, 13.8, 18.9, 21.3, 25.5, 28.8, 31.2,36.1, 63.8, 128.5, 145.2, 177.6 ppm

Example 9 Extraction of Sulfured Compounds from Naphtha

The procedure for the sulfured compound removal of the naphtha consistedof putting in contact one part of ionic liquid with 10 parts of naphtha(w/w) whose sulfur content has been determined previously. The mixtureis shaken vigorously during 10 minutes, the two phases are separated andthe sulfur content is determined in the naphtha after the extraction todetermine the percentage of total sulfur removal. The determination ofthe sulfur content was carried out by method ASTM-D 5453-05: StandardTest for Method Determination of Total Sulfur in Light Hydrocarbons,Fuels Motor and Oils by Ultraviolet Fluorescence.

The percentage of sulfur removed after the extraction liquid-liquid isshown in Table 2.

TABLE 2 Total sulfur removed % of total sulfur removed of the Ionicliquid gasoline LI-1 68 LI-2 72 LI-3 68 LI-4 70 LI-5 67 LI-6 66 LI-7 69LI-8 68 Total sulfur in the natural gasoline: 210 ppm Note: LI-1 =1-hexyl-3-methyl-imidazolium acetate LI-2 = 1-Octyl-3-methyl-imidazoliumacetate LI-3 = 1,2-dimethyl-3-octyl-midazolium acetate LI-4 =1-benzyl-3-methyl-imidazolium acetate LI-5 =1,2-dimethyl-3-butyl-imidazolium benzoate LI-6 = Butyl-isoquinoliniumbutanoate LI-7 = Dimethyl-diethyl ammonium stearate LI-8 =Butyl-pyridinium butanoate

From the Table No 2 is come off that the greater extraction sulfuredcompounds to start off of naphtha, was made with1-octyl-3-methyl-imidazolium acetate (Ionic liquid, LI-2). The tests ofrecovery and recycling were made with this compound.

LI-2 1-Octyl-3-methyl-imidazolium acetate Example 10 Recovering andRecycling of the Ionic Liquids

After each extraction the regeneration of the ionic liquids was realizedby a procedure which consists of three steps; in the first step theionic liquid was heated between 60 and 90° C., preferably of 75 to 85°C., in conditions of reduced pressure between 130 and 150 mmHg,preferably from 135 to 145 mmHg, for elimination of volatile compounds,in the second step, the ionic liquid was washed with solvents as ether,hexanes, heptanes, ether of petroleum or using mixtures of them in aproportion v/v between 1 and 15, preferably from 1 to 10; and in thethird step the solvent was eliminated under vacuum.

The Table 3 shows the results of the sulfur removal after 3 cycles ofregeneration and recycling of the LI-2, using original naphtha in eachcycle.

TABLE 3 Desulfurization of original naphtha using recovered ionicliquid. Extraction Sulfur removal Ionic liquid IL-2 cycle (%)

1-octyl-3-methyl-imidazolium acetate 1 2 3 72 70 67

As listed in Table 3, the ionic liquids can be used several times inremoving sulfur compounds, because the performance of sulfur removing isvery similar, indicating that they do not lose their physicochemicalcharacteristics during the extraction process and recovery

Quantitative desulfurization of naphtha was accomplished in threeconsecutives cycles of extraction (over 95%), using the ionic liquidsdescribed in this invention, as shown in Table 4.

TABLE 4 Total sulfur removed using the desulfurated naphtha of previousextraction Extraction Sulfur removal Ionic liquid IL-2 cycle (%)

1-octyl-3-methyl-imidazolium acetate 1 2 3 72 87 96

In Table 4 shown that with increasing the number of extraction cycles,increases the removal of sulfur, reaching values very close to the totalextraction (100%).

While various embodiments have been chosen to illustrate the invention,it will be understood that various changes and modifications can be madewithout departing from the scope of the invention as recited in theappended claims.

What is claimed is:
 1. A process for the desulfurization of ahydrocarbon feedstock containing sulfur compounds, which comprisescontacting said feedstock with a halogen-free sulfur extracting liquidconsisting essentially of an ionic liquid containing a heterocycliccation and a carboxylate anion and having the formula C⁺A⁻ wherein C⁺ isan isoquinolinium cation, and A⁻ is a carboxylate anion having theformula

where R₄ is selected from the group consisting of alkyl, cycloalkyl,alkenyl, benzylic and functionalized alkyl having 1 to 18 carbon atoms.2. The process of claim 1, wherein said contacting comprisesliquid-liquid extraction in which aliphatic and aromatic sulfurcompounds are removed from said feedstock.
 3. The process of claim 1,wherein the hydrocarbon feedstock is naphtha.
 4. The process of claim 1,wherein the hydrocarbon feedstock is selected from the group consistingof gasoline, diesel fuel, kerosene and heating oil.
 5. The process ofclaim 1, wherein said ionic liquid is butyl-isoquinolinium butanoate. 6.The process of claim 1, wherein said isoquinolinium cation has theformula

where R is selected from the group consisting of alkyl, cycloakyl,alkenyl, benzylic, and functionalized alkyl having 1 to 10 carbon atoms.7. A process for the desulfurization of a hydrocarbon feedstockcontaining sulfur compounds comprising the step of contacting saidfeedstock with a halogen-free sulfur extracting liquid consistingessentially of an ionic liquid containing a heterocyclic cation and acarboxylate anion, wherein said heterocyclic cation is an isoquinoliniumcation and its derivatives with substituents comprising benzylic,aromatic, cycloalkyl, alkenylic or aliphatic chains, which contain from1 to 10 carbon atoms.
 8. The process of claim 7, wherein saidcarboxylate anion has the formula

where R₄ is alkyl, cycloalkyl, alkenyl, benzylic and functionalizedalkyl having 1 to 8 carbon atoms.
 9. A process for the recovery andreuse of ionic liquid used for the removal of sulfur impurities fromhydrocarbons, said ionic liquid is halogen free comprising anisoquinolinium cation and a carboxylate anion, and containing sulfurcompounds, which comprises passing said ionic liquid containing sulfurcompounds in a first stage in which the ionic liquid is heated to atemperature in the range of 60 to 90° C., under conditions of reducedpressure in the range of 130 to 150 mm Hg and removing volatilecompounds, passing the resulting ionic liquid to a second stage in whichthe ionic liquid is washed with a solvent selected from the groupconsisting of diethyl ether, hexanes, heptanes, petroleum ether andmixtures thereof in a proportion v/v of 1 to 15 and removing the sulfurcompounds from the ionic liquid, and passing the solvent washed ionicliquid to a third stage in which the solvent is removed under vacuumconditions.
 10. The process of claim 9 in which the ionic liquid isheated to a temperature of 75 to 85° C. in the first stage under apressure of from 135 to 145 mmHg, and the proportion v/v of solvent usedin the second stage is 1 to
 10. 11. The process of claim 9, wherein saidhydrocarbon is naphtha.
 12. The process of claim 9, wherein saidisoquinolinium cation has the formula

where R is selected from the group consisting of alkyl, cycloakyl,alkenyl, benzylic, and functionalized alkyl having 1 to 10 carbon atoms.13. The process of claim 12, wherein said carboxylate anion has theformula

where R₄ is alkyl, cycloalkyl, alkenyl, benzylic and functionalizedalkyl having 1 to 8 carbon atoms.